The invention relates to roll-tarp systems and to crank assemblies such as, for example, those classed in class 296, subclasses 98–100.
Various types of truck, trailer and container bodies are designed to be loaded through an open top. Such bodies are typically used to haul grain, earth or refuse. It is desirable to use tarpaulins or other coverings to close the open tops of such containers. The tarpaulins serve to shelter the contents of trucks, trailers or containers against the elements and to maintain the contents in the containers when the containers are exposed to high winds or moved from place to place.
Several systems are known for covering truck, trailer and containers with tarpaulins. Typically, the covering is unrolled from a long tube by associated hardware from an open position in which the covering is entirely wrapped around the tube, exposing the interior of the container, to a closed position in which the covering is spread over the top of the container. These systems tend to use fiberglass or metal bows to span the width of the opening and support the covering at regular parallel spaced intervals along the length of the open top.
An example of an excellent tarp system that has become extremely popular and widely used commercially is shown in U.S. Pat. No. 4,302,043 to Dimmer et al. assigned to Wahpeton Canvas Company, Inc. of Wahpeton, S. Dak., which sells that system commercially under the trademark SHUR LOK. As shown in the Dimmer et al reissue patent, a covering is attached along one lengthwise edge to one edge of the container and along an opposite lengthwise edge to a roll tube that, in turn, is connected at one end by a universal joint to a crank. The universal joint and crank can be removably attached to the roll tube by a spline and pin or other similar mechanism to allow customization. An operator at ground level can turn the crank causing the universal joint to rotate the roll tube to cause the cover to roll up lengthwise on the tube to uncover the top of the trailer or container or to unroll lengthwise from the tube to cover the top of the trailer or container. The end of the roll tube to which the universal joint and crank arm are attached can be described as the active end because the torque or turning force is applied there. Conversely, the opposite end can be described as the passive end because the torque is applied to the opposite end indirectly through the length of the tube.
The Shur Company roll-tarp system has found such widespread acceptance among truck owners because it is relatively quick to use and usually looks neat and uncluttered when latched in place. Since the Shur Company roll-tarp system latches under a ledge at the top of the trailer, the front, sides and rear of the truck are untouched and can have markings and signs that are not cluttered by tie down straps and hooks prevalent in many other tarp systems. Even though roll-tarps are desirable for their ease of use and neat appearance, there are some areas where the roll-tarp system might be improved. When large or uneven loads are present such that the top of the load is higher than the bows, which is a clear misuse of the tarp system, the tarp must pass over a longer distance in covering the “over-bow” portion of the load relative to the remainder of the container and this can result in the tarp being tight in the area over-bow but loose everywhere else unless the roll tube is excessively stressed by over-twisting the crank and applying a huge torque to the roll tube to pull very hard on the tarp to try to stretch the tarp sufficiently to put the roll tube into a proper latched position under a latch plate on an upper side edge of the trailer. This is a risky action, which operators should recognize as being risky, but since truckers are often paid by the load or weight, when they have bulky materials or light materials there is a strong financial incentive to try to maximize the load even to the extent of temporary unsafe conditions. This can cause all kinds of problems, but since truckers are paid by load or weight, they may nevertheless feel compelled by financial considerations to have loads that extend over the bows in some portion of the container. To maximize the load, the trucker may start with an overbow load and think that by rocking the trailer forward and back (by accelerating and braking or jerking the clutch) to try to jerk the load into even distribution, but that is not usually very successful, especially if the load is sticky. Even if successful, that jerking obviously adds wear and tear on drive trains, transmissions, brakes and tires. Another solution truckers might try to spread out loads that extend above the bows is to climb up on the edge of the trailer with a shovel and balance precariously while trying to level the load with a shovel. However, that risky maneuver raises the possibility of slip and fall injury to the trucker during this climbing, balancing, and shoveling, particularly if the weather is icy, snowy, or rainy, or if the load is wet and slippery. So, a trucker may decide that the best compromise is to just crank real hard on the tarp to try to stretch it over the over-bow load so that risky climbing up the trailer or destructive jerking of the drive train can be avoided. This overstressing requires tremendous torque because tarps do not stretch easily. A typical torque for normal tightening of a roll-tarp might be specified as 60 foot-pounds of pressure on the roll bar, as measured one foot out on the crank handle from the roll bar. An over-bow load might take 200 pounds or more of force on the crank handle to rotate the roll tube sufficiently to latch for a sufficient distance that the trucker feels it probably won't come loose during travel, and even then there is likely to be a portion of the roll bar not fully latched. Since 200 pounds or more of force on the crank handle is a lot of force even for a strong trucker. Unless the trucker weighs well over 200 pounds, that force may be sufficient to lift the trucker off the ground, which is obviously undesirable. If the crank handle is slippery, any slip under that kind of pressure may result in the handle slipping out of the operator's hand and then being whipped around viciously with possible injury to the operator or others nearby. Also, since the crank arm might typically be 10 feet long, 2000 foot pounds or more of torsional force might actually be put on the U-joint and roll tube by this over-bow tarp tightening action, and this can lead to damage or even breaking of the roll tube or crank or U-joint, with consequent risk to everyone around, including adjacent vehicles, but especially to the operator himself. If the roll bar breaks, it may break several feet forward of the back of the truck, and this requires repair and welding of a new end on the roll bar at significant expense and significant delay to the trucker and with resultant delay in delivery of the load. If the roll bar does not break, it will still be in the overstressed state and is also now “cocked” so that if an unsuspecting person unlatches the crank to roll up the tarp to uncover the load, there could be an undesirable whipping action of the crank as it seeks to rotate to relieve 2000 foot pounds or more of stress. Also, the operator of crank handles which bend into locking position force the operator to use a shortened portion of the handle to lock the handle into position and must let go with one hand to use the other hand to operate any pin or lock. This accentuates the risk of the crank slipping and popping back at the operator. Another problem created by oversize loads is that if the load settles, the stretched tarp may become loose enough to flap in the wind like a flapping sail, increasing wear on the tarp and shortening its useful life. If the loads settles sufficiently, the tarp might even come unlatched and act like a giant spinnaker or parachute, pulling the crank handle and mount right off the back or side of the trailer and flipping it around with possible damage to adjacent vehicles. Roll-tarps work well when used properly and are an excellent accessory for open top trailers and instructions from manufacturers typically warn against over-bow tarping, but for the above reasons the warning may be disregarded.
Rather than providing a warning that users will ignore, it would therefore be of significant benefit to the advancement of technology in the roll tarp industry to introduce design improvements to attempt to minimize the risks associated with even such clear misuse of the tarp system by helping minimize excessive torque on the roll-tarp systems noted above through design improvements. Even though the manufacturer of the tarp system may not be responsible for such misuse of its systems, it is desirable to minimize risk even in the event of misuse.
In normal operation the tarp may loosen slightly during road travel. This loosening can be due to various reasons such as for example settling of the load, self-straightening of the tarp, or unwrinkling of the tarp. So, it is sometimes desirable or even required to further tighten a previously tightened tarp. It would be desirable to have some means of automatically tightening the tarp without the operator having to constantly monitor the tarp, notice when it is getting loose, stop the truck, get out, loosen the crank, crank the roll bar to tighten the tarp, refasten the crank, and get back in the cab. Motorized tarp covers may allow simpler tightening of loose roll bars but such tightening is not generally automatic and requires the operator to notice the need for tightening and then to activate the motorized crank.
Further, there is a need to have any roll tarp securing device be improved so that even in the event of failure the operative parts do not come loose from the overall assembly. Loose parts could pose a hazard to other motorists.
There is, in summary, a need for an improved roll-tarp system to increase the safety and reliability for truckers and other roll-tarp users.